An automatic transmission includes a planetary gear mechanism and a plurality of frictional engagement elements, and switches a gear position by switching an engagement state of each frictional engagement element such that a desired gear position is obtained. In some of the frictional engagement elements, a required engagement capacity differs according to the gear position, but when a working oil pressure supplied to such a frictional engagement element is varied according to the required engagement capacity, hydraulic control becomes complicated.
Hence, in an automatic transmission disclosed in JP5-288264A, two hydraulic chambers to which working oil pressure is supplied are provided individually for a single frictional engagement element, and by supplying oil pressure to one or both of the hydraulic chambers in accordance with the required engagement capacity, the engagement capacity can be varied without increasing the complexity of the hydraulic control.